1. Field of the Invention
This invention relates to impact hammers for rotary stage loader impact crushers and, more particularly, to impact hammers which are affixed to the rotary head of such a crusher.
2. Description of the Prior Art
The longwall method of underground coal mining, which was implemented during the latter half of the twentieth century, is generally considered to represent the most revolutionary advance in coal mining technology in history. Longwall mining now accounts for about 31% of underground coal production. There are about 100 longwall operations in the United States, with most of them being in Appalachia. In longwall mining, a cutting head moves back and forth across a vertical face at one end of a seam of coal being mined. The vertical face, or “wall”, typically has a width within a range of about 250 to 400 meters, and a height within a range of 1 to 2 meters. The seam of coal may be several kilometers in length. The cut coal falls onto a flexible conveyor for removal. Longwall mining is done under hydraulic roof supports (shields) that are advanced as the seam is progressively cut away. The roof in the mined out areas falls as the shields advance. About ninety percent of the coal within a seam is recoverable using the method. Stage loader crushers, which are generally of the rotary impact type, are used as part of the longwall mining system to crush lump coal and oversize rock for easier conveying and to prevent jamming of the conveyer system. Such crushers are manufactured by companies such as Joy Mining Machinery, Inc. And McLanahan Corporation. The crushers typically utilize a rotary drum onto which impact hammers having tungsten carbide inserts are affixed. Hammers produced by original equipment manufactures (OEMs) are often affixed to a rotary drum with a roll pin inserted through a mounting post. However, because the roll pin represents a common failure point, bolting of the hammer to the drum has become increasingly common. The hammer generally has a hollow mounting post so that a bolt can be inserted through the hollow post and then secured with a nut to an anchor on the rotary drum. Although the bolted design constitutes a significant improvement over the roll-pin secured hammer, the bolt is still prone to failure.
Another problem with OEM hammers is that the steel hammer blank, to which tungsten carbide inserts are welded, is subject to rapid wear.